This SBIR aims to develop a quantitative in vivo zebrafish hair cell assay that can be used to identify potential otoprotective agents. Zebrafish is a useful animal model for identifying otoprotectants since neuromast hair cells, which are located in stereotypical positions in the head and trunk region, are structurally and functionally similar to the inner ear hair cells in mammals. Human hair cells can be damaged by infection, aging, genetic disease, noise or treatment with drugs, including anti-cancer drugs and antibiotics. Drug-induced ototoxicity can ultimately lead to sensory hair cell death, causing hearing loss and vestibular disorders. Although hearing aids are useful for some patients with hearing loss, there is no effective therapy. Current therapeutic strategies include application of growth factors and other agents to promote cell survival, and systemic application of drugs to prevent activation of programmed cell death. The proposed zebrafish assay will facilitate development of protective treatments to minimize ototoxic side effects and increase the clinical utility of current medications. Hearing loss from ototoxic therapies, aging, environmental and genetic factors, represents a significant market with unmet medical needs. In the United States, the market for hearing loss is currently at $30 billion and is expected to increase rapidly in the next several decades. [unreadable] [unreadable] [unreadable]